Referring to FIGS. 1A and 1B, FIG. 1A is a circuit diagram illustrating a conventional buck voltage converting apparatus 100, and FIG. 1B illustrates waveforms of the signals of the buck voltage converting apparatus 100. The buck voltage converting apparatus 100 includes transistors Q1 and Q2, an inductor L1 and a capacitor C1. The transistors Q1 and Q2 are alternately turned on or off based on complementary control signals UGATE and LGATE which are respectively received by the transistors Q1 and Q2, and an input voltage is converted via the inductor L1 to generate an output voltage VOUT, wherein the output voltage VOUT is used to drive a load RL.
Referring to FIG. 1B, at a time point T1, a current IRL required by the load RL drops rapidly (the load RL is changed from heavy load to light load), and a dropping rate of a current IL1 stored in the inductor L1 does not keep up with the change of the load RL. Meanwhile, a power storage in the capacitor C1 is charged rapidly by receiving the current IL1 on the inductor L1, and an overshoot on the output voltage VOUT is generated for a rapid increase of the output voltage VOUT. The overshoot of the output voltage VOUT may damage circuit devices on the buck voltage converting apparatus 100 and/or the load RL and influence operations of related products.